Can confirm it works! Just got CD-i games up-and-running in Mame 215 and Launchbox using the above tutorial and whatever else I could scrounge up around the net. They definitely need to make an updated video for this, took me hours to figure it out with bits and pieces of outdated info from several different sources. The key take-aways for CD-i emulation in Mame are;
1: Import your Phillips CD-i roms into Launchbox (CHD format is preferred for your roms, bin/cue files don't seem to work well. If you already have bin/cue files you can convert them to CHD).
2: Make sure you have correct CD-i bios file (cdimono1) in your Mame > roms folder.
3: Set Mame as your emulator. Make sure to uncheck the three boxes in the 'Emulator edit' tab.
4: Under 'Associated Platforms' tab add the platform name (Phillips CD-i) and check 'Default Emulator' box.
5: Under 'Default Command-Line Parameters' type 'cdimono1 -cdrm'
Hopefully that's helpful to somebody